1. Field of the Invention
The present invention relates to a method for breaking sheets and other brittle materials, more particularly a method for laser scoring of flat glass sheets.
2. Technical Background
Lasers have been used heretofore for separating sheets of brittle material, especially flat sheets of glass, by propagating a so-called blind crack across a glass sheet to break the sheet into two smaller glass sheets. This partial crack, which extends partway through the depth of the glass sheet, essentially operates as a score line. The sheet is then separated into two smaller sheets by mechanical breaking along the line of the score line.
In one embodiment, a small nick or scribe is made at one side of the glass sheet, and this nick or scribe is then propagated in the form of a partial crack through the glass sheet using a laser. The laser is then contacted with the glass sheet in the area of the nick or scribe and the laser and glass sheet are moved relative to one another, so that the laser travels in the desired path of the score line. A stream of fluid coolant is preferably directed at a point on the heated surface of the glass just downstream from the laser, so that after the laser has heated a region of the glass sheet, the heated region is quickly cooled. In this way, the heating of the glass sheet by the laser and the cooling of the glass sheet by the fluid coolant creates stresses in the glass sheet which cause the crack to propagate in the direction that the laser and coolant have traveled.
The development of such laser scoring techniques has resulted in some good results in terms of quality break edges, making them potentially useful in the manufacture of liquid crystal and other flat panel display panel substrates, where the quality of edge breaks is desirably very high. Recent advances have shown that the use of a multimoded laser (e.g. a D-mode laser) was effective in reducing the optical power impinging on the glass at the center of the beam, thus producing a more even temperature profile across the spot on the glass where the beam impinges. However, multimoded lasers are often higher in cost, require greater maintenance, and can be significantly more unwieldy than sealed beam single-mode lasers.
It would be desirable to design a laser scoring process which is capable of high scoring speeds, e.g., on the order of at least 300 mm/second, more preferably at least 500 mm/second, and most preferably at least 1000 mm/sec, which would simplify the scoring and braking processes for the production of flat panel display substrates.